Filler on the basis of particulate composite

ABSTRACT

Particulate composite material with an average particle size of 20 to 50 μm and a maximum content of particles with a size of &lt;10 μm of 10 wt.-% and its use for the preparation of dental materials.

[0001] The invention relates to fillers on the basis of particle-shapedcomposite materials, which have a defined grain size distribution andcontain only a small proportion of fine-grain particles.

[0002] As a rule, modern dental materials contain a liquid,polymerizable binder in the form of monomers or monomer mixtures as anessential component. It is known that, during the polymerization of suchbinders, usually a more or less strongly pronounced volume contractiontakes place (cf. R. R. Sadhir, R. M. Luck, Expanding Monomers-Synthesis,Characterization and Application; CRC Press, Boca Raton 1992, pages3ff). The shrinkage is attributable to the development of covalent bondsbetween the monomer molecules during polymerization, whereby thedistance between the molecules is decreased. In the unpolymerized state,the molecules are predominantly held together by Van der Waals forces,which result in a greater intermolecular distance.

[0003] During the preparation of pre-shaped parts, the polymerizationshrinkage has a very disadvantageous effect on the dimensional stabilityand the mechanical properties of the moulded bodies. In the case ofadhesives and gluing compounds, the polymerization shrinkage adverselyaffects the adhesion properties and the bonding strength, whichdeteriorates the adhesion between restoration material and the naturaltooth substance of dental materials. Cracks form which encourage thedevelopment of secondary caries.

[0004] To reduce the polymerization shrinkage of dental materials, theuse of high-molecular-weight monomers or prepolymers, the use ofmonomers which can be polymerized by ring-opening polymerization, theaddition of inert, porous or expanding fillers or gas-releasing systemswas described.

[0005] When selecting suitable filling materials, particle size assumesspecial importance. Large particle diameters produce materials with poorpolishability and unacceptable abrasion, while filling materials havinga small particle size show a strong thickening effect, whereby the needfor monomers is increased and as a result of this the polymerizationshrinkage is increased. In addition, the incorporation of the filler ismade more difficult by the high viscosity and the maximum amount offiller is limited.

[0006] Tooth-filling compositions are known from DE-OS 14 92 040 whichcontain as filler glass beads with a particle size in the range of 5 to100 μm. Glass fibres are used in addition to fill intermediate spaces.Because of their spherical shape, the beads are said to guarantee anoptimal breaking strength and a low abrasion effect. The colour of thecomposition is said to automatically match the colour of the naturaltooth material upon curing.

[0007] DE 24 03 211 A1 discloses dental materials in which exclusivelymicrofine, inorganic fillers (microfillers) on the basis of silicondioxide are used, the particle size of which is below 700 nm.

[0008] According to a particularly preferred version, at least 50 wt.-%of the filler have a particle size of 10 to 400 nm. Surprisingly,filling materials with good transparency and polishability as well asexcellent physical properties are obtained.

[0009] DE 27 05 220 A1 proposes transparent dental materials with highcompressive strength in which a fine-particled filler is used with agrain distribution such that 70-95% of the particles have a grain sizeof 0.7 to 25 μm and 5-30% of the particles have a grain size of 0.2 to0.7 μm. Moreover, the filler can contain particles with a smallerdiameter than 0.2 μm in an amount of up to 5 wt.-%. The average grainsize of the fine-particled fillers is given as 1-5 μm. According to theexamples, raw α-quartz is heated and is ground using a specific method.

[0010] EP 0 475 239 A2 discloses dental materials which contain asfiller a mixture of amorphous, spherical particles of silicon dioxideand up to 20 mol.-% of an oxide of at least one element of groups I; II,III and IV of the periodic system with a refractive index of 1.50 to1.58 and with an average primary particle size of 0.1 to 1.0 μm, andquartz, glass ceramic or glass powder or their mixtures with arefractive index of 1.50 to 1.58 and with an average particle size of0.5 to 5.0 μm. The materials are characterized by a high transparencyand good polishability.

[0011] U.S. Pat. No. 5,356,951 discloses dental materials which containas filler a mixture of an organic-inorganic composite filler with anaverage particle size of 5 to 50 μm, glass powder with a maximumparticle size of 10 μm and an average particle size of 0.1 to 5 μm and afine-particled filler with a particle size of 0.01 to 0.04 μm. Thecomposite filler is for its part filled with glass powder which has amaximum particle size of 10 μm and an average particle size of 0.1 to 5μm. The materials are said to be characterized by a smooth surface, alow polymerization shrinkage and improved physical properties.

[0012] DE 198 23 530 A1 discloses dental materials which can contain asfiller an organic-inorganic composite material, which has an averageparticle size of 5 to 50 μm and for its part is filled with an ultrafineinorganic filler with an average particle size of 0.01 to 0.04 μm. Thedental materials are polymerized applying pressure and heat and thenprocessed further to dental restorations by milling. These are said tobe characterized by good mechanical properties and be free fromunpolymerized monomer.

[0013] EP 0 983 762 A1 discloses dental materials which contain asfiller a mixture of organic-inorganic composite filler with an averageparticle size of 5 to 50 μm, particular filler with an average particlesize of 20 μm or less and optionally glass powder with a maximumparticle size of 5 μm and an average particle size of 0.5 to 2 μm. Thecomposite filler is prepared by curing a mixture of a particular fillerwith an average particle size of 20 nm or less and a methacrylate oracrylate monomer with a viscosity of 60 cP or more and pulverising thecured mixture. The materials are said to be characterized by goodpolishability and good mechanical properties and have a smoothness andtransparency corresponding to the natural tooth.

[0014] In spite of the numerous dental materials described in the priorart and in spite of the sometimes significant improvements which wereachieved with regard to certain material properties, conventional dentalmaterials mostly still have a polymerization shrinkage of 2.3 to 2.8%.There is thus still a requirement to further reduce the polymerizationshrinkage of dental materials without adversely affecting the otherproperties.

[0015] The object of the invention is accordingly to preparepolymerizable compositions which have a low polymerisation shrinkage andgood other properties such as transparency and polishability.

[0016] This object is achieved by polymerizable compositions whichcontain a new type of filler on the basis of particulate compositematerial. This composite filler has an average particle size of 20 to 50μm and contains at most 10 wt.-% particles with a grain size of <10 μm.The percentage relates to the mass of the composite filler. By acomposite material is meant a material on the basis of polymerizableorganic binder and inorganic fillers.

[0017] Surprisingly it was found that the polymerization shrinkage ofpolymerizable compositions can be clearly reduced by using compositefillers with the stated grain-size distribution. In addition, thecompositions are characterized by good polishability, surface smoothnessand abrasion after curing in spite of their comparatively high contentof coarse-particled filler.

[0018] Basically, composite fillers are preferred which contain as lowas possible a proportion of finely particulate material, in particularat most 8 wt.-% and particularly preferably at most 6 wt.-% particleswith a size of <10 μm. Composite fillers with an average particle sizeof 30 to 40 μm are further preferred. The maximum particle size of thecomposite fillers is preferably 70 μm, i.e. the material contains lessthan 5 wt.-%, particularly preferably less than 1 wt.-% particles with asize of more than 70 μm.

[0019] By average particle size is meant the numerical average, unlessstated otherwise. This results from the frequency distribution aftergrading.

[0020] According to the invention, particulate composite materialssuitable as composite filler can be prepared for example by mixingorganic binder, filler and optionally polymerization initiator, curingand then grinding of the mixture. The ground product is, if necessary,graded, in order to obtain filler with the desired grain-sizedistribution.

[0021] Milling can take place in conventional mills, for example in aball mill, air-jet mill, impact mill or vibration mill. The compositematerial can be previously broken down in for example a conical crusherbefore the actual grinding.

[0022] The embodiments show that a considerable proportion of finelyparticulate material with a particle diameter of <10 μm is formed duringnormal grinding of composite materials. This is separated according tothe invention, for example by grading, such as flow sorting, screening,wind-sifting, optionally in combination with electrostatic processes,flotation, sedimentation, electrostatic or magnetic separation orsieving. Suitable processes are described in Ullmanns Encyklopädie derTechnischen Chemie, Volume 2 (1988), Unit Operations.

[0023] Suitable as organic binder for the preparation of the particulatecomposites are all binders curable by polymerization, in particularethylenically unsaturated polymerizable binders, e.g. monomers, such asmonofunctional or polyfunctional methacrylates which can be used aloneor in mixtures. Preferred examples of these compounds are methylmethacrylate, isobutyl methacrylate, cyclohexyl methacrylate,tetraethylene glycol dimethacrylate, triethylene glycol dimethacrylate,diethylene glycol dimethacrylate, ethylene glycol dimethacrylate,polyethylene glycol dimethacrylate, butanediol dimethacrylate,hexanediol dimethacrylate, decanediol dimethacrylate, dodecanedioldimethacrylate, bisphenol-A-dimethacrylate, trimethylol propanetrimethacrylate,2,2-bis-[4-(2-hydroxy-3-methacryloxypropoxy)-phenyl]-propane(bis-GMA) aswell as the reaction products of isocyanates, in particular di- and/ortriisocyanates and OH-group-containing methacrylates. Examples of thisare the reaction products of 1 mol hexamethylene diisocyanate with 2 mol2-hydroxyethylene methacrylate, of 1 mol tri(6-isocyanate-hexyl) biuretwith 3 mol 2-hydroxyethyl methacrylate and of 1 mol2,2,4-trimethylhexamethylene diisocyanate with 2 mol 2-hydroxyethylmethacrylate, called urethane dimethacrylates in the following. Thebinder content varies between 10 and 80 wt.-% relative to the mass ofthe composite material, preferably 10 to 30 wt.-%.

[0024] Urethane dimethacrylate (UDMA), i.e. the reaction product of 1mol 2,2,4-trimethylhexamethylene diisocyanate with 2 mol 2-hydroxyethylmethacrylate, 1,10-decanedioldi(meth)acrylate,bisphenol-A-dimethacrylate, ethoxylated bisphenol-A-dimethacrylate andmixtures of these monomers are particularly preferred monomers.

[0025] In order to initiate the polymerization, the mixtures contain apolymerization initiator, for example an initiator for the radicalpolymerization. Depending on the type of initiator used, the mixturescan be polymerized cold, by light or preferably hot.

[0026] The known peroxides such as dibenzoyl peroxide, dilauroylperoxide, tert.-butyl peroctoate or tert.-butyl perbenzoate can be usedas initiators for the hot polymerization, but α,α′-azo-bis(isobutyroethylester), benzopinacol and 2,2′-dimethylbenzopinacol arealso suitable.

[0027] As initiators for the photopolymerization, e.g. benzophenone andits derivatives as well as benzoin and its derivatives can be used.Further preferred photoinitiators are the α-diketones such as 9,10phenanthrenequinone, diacetyl, furil, anisil, 4,4′-dichlorobenzil and4,4′dialkoxybenzil. Camphorquinone is particularly preferably used.

[0028] 2,4,6-trimethylbenzoyldiphenyl phosphine oxide is particularlysuitable as initiator for the polymerization initiated by UV light. UVphotoinitiators can be used alone, in combination with an initiator forvisible light, an initiator for the cold curing and/or an initiator forhot curing.

[0029] Photoinitiators are preferably used together with a reducingagent. Examples of reducing agents are amines such ascyanoethylmethylaniline, triethylamine, triethanolamine,N,N-dimethylaniline, N-methyldiphenylamine, N,N-dimethyl-sym.-xylidineand N,N-3,5-tetramethylaniline and 4-dimethylaminobenzoic ethyl ester.

[0030] Radical-delivering systems, e.g. benzoyl or lauroyl peroxidetogether with amines such as N,N-dimethyl-sym.-xylidine orN,N-dimethyl-p-toluidine are used as initiators for the coldpolymerization. Dual-curing systems can also be used for catalysis, e.g.photoinitiators with amines and peroxides.

[0031] The initiators are normally used in an amount of 0.01 to 5 wt.-%relative to the total mass of the mixture.

[0032] Suitable as inorganic filler are in particular quartz, glassceramic, glass powder cr mixtures of these, preferably glass powder andquite particularly preferably barium glass powder and/or strontium glasspowder, the average particle size of these powders preferably being inthe range of 0.4 to 1.5 μm and in particular in the range of 0.7 to 1.0μm. Quartz, glass ceramic and/or glass powder are preferably used in anamount of 10 to 80 wt.-%, in particular 40 to 85 wt.-% relative to thetotal mass of the mixture.

[0033] Moreover, the composite filler can contain fillers for achievingan increased X-ray opacity. The average particle size of theX-ray-opaque filler is preferably in the range of 100 to 300 nm, inparticular 180 to 300 nm. Suitable as X-ray-opaque fillers are, e.g. thefluorides described in DE 35 02 594 A1 of the rare earth metals, i.e.the trifluorides of elements 57 to 71. A particularly preferably usedfiller is ytterbium fluoride, in particular ytterbium trifluoride withan average particle size of approx. 300 nm. The amount of theX-ray-opaque filler is preferably 10 to 50 wt.-%, particularlypreferably 20 to 30 wt.-%.

[0034] In addition, precipitated mixed oxides, such as for exampleZrO₂/SiO₂, can be used as fillers. Mixed oxides with a particle size of200 to 300 nm and in particular approx. 200 nm are preferred. The mixedoxide particles are preferably spherical and have a uniform size. Themixed oxides preferably have a refractive index of 1.52 to 1.55. Themixed oxides can be used as sole filler or in combination with otherfillers. The precipitated mixed oxide is preferably used in an amount of20 to 90 wt.-%, particularly preferably 25 to 75 wt.-% and quiteparticularly preferably 40 to 75 wt.-%.

[0035] The fillers are preferably silanized to improve the adhesionbetween filler and organic matrix. α-Methacryloxypropyl trimethoxysilane is particularly suitable as adhesion promoter. The amount of theadhesion promoter used depends on the type and the BET surface of thefiller.

[0036] In addition to the already named substances, the mixtures cancontain additives, such as stabilizers and polymerization inhibitors.These are preferably used in an amount of 0.01 to 2 wt.-%.

[0037] The total amount of inorganic filler is preferably in the rangeof 20 to 90 wt.-%, in particular 60 to 88 wt.-% relative to the totalmass of the composite filler.

[0038] A preferred mixture for the preparation of the composite filleraccordingly has the following composition:

[0039] (a) 10 to 80 wt.-%, preferably 10 to 30 wt.-% organic binder;

[0040] (b) 0.01 to 5 wt.-%, preferably 0.03 to 5 wt.-% and in particular0.5 to 2 wt.-% polymerization initiator;

[0041] (c) 20 to 90 wt.-%, preferably 60 to 88 wt.-% inorganic filler.

[0042] As filler (c) the mixture preferably contains

[0043] (c1) optionally 10 to 80 wt.-%, preferably 40 to 65 wt.-% glasspowder; and/or

[0044] (c2) optionally 10 to 50 wt.-%, preferably 20 to 30 wt.-%X-ray-opaque filler; and/or

[0045] (c3) optionally 20 to 90 wt.-%, preferably 25 to 75 wt.-%,particularly preferably 40 to 75 wt.-% of precipitated mixed oxide.

[0046] All figures relate in each case to the total mass of the mixture.The composition can contain one of the components (c1), (c2) or (c3) ora mixture thereof as filler. Compositions are preferred which contain afiller of type (c1), alone or particularly preferably in combinationwith one of the components (c2) to (c3).

[0047] After curing, grinding and grading, the composite particles arepreferably treated with a suitable adhesion promoter. This reacts withthe free surface of the filler of the composite material which areexposed when grinding the composite, and thus improves the adhesionbetween filler and organic matrix. The above-mentioned silanes arepreferred as adhesion promoter.

[0048] The particulate composite materials according to the inventionare particularly suitable as fillers for polymerizable compositions,i.e. compositions which, along with the particulate composite material,contain at least one polymerizable monomer and/or prepolymer and atleast one polymerization initiator. The proportion of the particulatecomposite material is preferably in the range of 20 to 90 wt.-%,particularly preferably 25 to 70 wt.-% and quite particularly preferably30 to 50 wt.-%. The amount of organic binder is preferably 10 to 80wt.-%, particularly preferably 10 to 30 wt.-%, the amount of theinitiator being 0.01 to 5 wt.-%, in particular 0.1 to 1 wt.-%.

[0049] For the preparation of polymerizable compositions, compositefillers with a density of 1.5 to 2.5 g/cm³, in particular 1.8 to 2.2g/cm³ are preferred. The relatively low density requires a high fillervolume proportion in the polymerizable composition and effects anadditional decrease of the polymerization shrinkage.

[0050] Along with the composite filler, the polymerizable compositionspreferably in addition contain further particulate inorganic filler, inparticular quartz, glass ceramic, glass powder or mixtures of these,particularly preferably glass powder, quite particularly preferablybarium glass powder and/or strontium glass powder. The average particlesize of the quartz, glass ceramic and/or glass powder is preferably inthe range of 0.4 to 2 μm, particularly preferably 0.4 to 1.5 μm andquite particularly preferably 0.7 to 1.0 μm. The proportion of thequartz, glass ceramic and/or glass powder is preferably 20 to 70 wt.-%,particularly preferably 25 to 50 wt.-% and quite particularly preferably30 to 40 wt.-% relative to the total mass of the composition.

[0051] The compositions can contain moreover one of the above namedprecipitated mixed oxides and/or one of the above named fillers forincreasing the X-ray opacity, such as for example ytterbium trifluoride.The mixed oxide is preferably used in an amount of 20 to 70 wt.-%, theproportion of the X-ray-opaque filler is preferably in the range of 1 to10 wt.-%, particularly preferably 1 to 5 wt.-%. The particle size of theX-ray-opaque filler is preferably in the range of 100 to 300 nm, inparticular 180 to 300 nm. Preferred mixed oxides are precipitatedSiO₂/ZrO₂-mixed oxides, which preferably have a particle size of 200 to300 nm and in particular approx. 200 nm.

[0052] Moreover, the compositions can contain an organically modifiedlayered silicate for the establishment of the Theological behaviour. Thelayered silicate is preferably used in an amount of 0.05 to 5 wt.-%,particularly preferably 0.1 to 1 wt.-%. The sum of the proportions ofthe X-ray-opaque filler and the layered silicate is preferably at most 5wt.-%.

[0053] The total amount of the additional inorganic filler of thepolymerizable composition is preferably in the range of 0.05 to 85wt.-%, in particular 0.1 to 56 wt.-%. According to a particularlypreferred version, the polymerizable composition is essentially freefrom filler with a particle size of <100 nm. The inorganic filler ispreferably treated with an adhesion promoter, thus for examplesilanized.

[0054] In addition, the polymerizable compositions can contain normaladditive and adjuvants, preferably in an amount of 0.01 to 2 wt.-%.

[0055] The substances described above as components of the compositefiller are suitable as organic binders, polymerization initiators,additional fillers and additives. Preferred monomers for the preparationof the polymerizable compositions are benzyl methacrylate, ethoxylatedbisphenol-A-dimethacrylate, tetrahydrofuryl methacrylate and inparticular bisphenol-A-dimethacrylate, ethoxylatedbisphenol-A-dimethacrylate according to the formula (1) with n=1 and m=2and the reaction product of 2 mol hydroxyethyl methacrylate (HEMA) and 1mol hexamethylene diisocyanate.

[0056] Accelerators, dyes, pigments, UV-absorbers, optical whiteners andlubricants are considered as additives in addition to the above namedmaterials. Compositions which contain a photoinitiator are preferred.

[0057] The polymerizable compositions according to the inventionpreferably have the following composition:

[0058] (i) 10 to 80 wt.-%, preferably 10 to 30 wt.-% organic binder;

[0059] (ii) 0.01 to 5 wt.-%, preferably 0.1 to 1 wt.-% polymerizationinitiator;

[0060] (iii) 20 to 90 wt.-%, preferably 25 to 75 wt.-% composite filler;and

[0061] (iv) optionally 20 to 70 wt.-%, preferably 25 to 50 wt.-% quartz,glass ceramic, glass powder or a mixture of these;

[0062] (v) optionally 1 to 10 wt.-%, preferably 1 to 5 wt.-%X-ray-opaque particular filler;

[0063] (vi) optionally 20 to 70 wt.-% of precipitated mixed oxide;

[0064] (vii) optionally 0.05 to 5 wt.-%, preferably 0.1 to 1 wt.-%layered silicate;

[0065] (viii) optionally 0.01 to 2 wt.-% further additives.

[0066] The polymerizable compositions are suitable in particular asdental materials. The term dental material is taken to meantooth-filling materials, materials for inlays or onlays, tooth cements,facing materials for crowns and bridges, materials for false teeth orother materials for prosthetic, preservative and preventive dentistry.

[0067] The dental material according to the invention preferably servesas tooth-filling material. Tooth-filling materials are also prepared astwo-component materials which cure cold after mixing. The composition issimilar to that for the light-curing materials, but instead of thephotocatalysts, e.g. benzoyl peroxide is worked into the one paste ande.g. N,N-dimethyl-p-toluidine into the other paste. The result of mixingroughly equal parts of the two pastes is a tooth-filling material whichcures fully in a few minutes.

[0068] If the amine is left out of the last named materials and e.g.only benzoyl peroxide is used as catalyst, a hot-curing dental materialis obtained which can be used for the preparation of an inlay or falseteeth. For the preparation of an inlay, an impression is taken of thecavity in the patient's mouth and a plaster mould is prepared. The pasteis introduced into the cavity of the plaster model and the whole ispolymerized under heat in a pressure pot. The inlay is removed, workedup and then cemented into the cavity in the patient's mouth.

[0069] The invention relates not only to the dental material, but alsoto the finished parts prepared from this, e.g. false teeth, shells,inlays etc.

[0070] The invention is explained in more detail in the following usingexamples.

EXAMPLE 1 Preparation of a Particulate Composite Material (CompositeFiller)

[0071] For the preparation of a particulate composite material, thefollowing components were mixed together in the stated amounts, and themixture cured at 100° C. for 24 hours, then coarsely broken into piecesand then finally ground in a ball mill. The average grain size was 21μm. The fine (<10 μm) and the coarse (>70 μm) grains were removed byscreening. As a result of screening, the average particle size shifts to37 μm. The grain-size distribution before screening is shown in FIG. 1,the grain-size distribution after screening is shown in FIG. 2. Half ofthe material was then silanized with 5 wt.-% methacryloxypropyltrimethoxy silane and 2 wt.-% in water. Monomer mixture for thepreparation of the composite filler: 1,10-decandiol-dimethacrylate 30wt. % Bisphenol-A-dimethacrylate 39.95 wt. % Urethane dimethacrylate(UDMA) 27 wt. % Benzoyl peroxide (50%) 3 wt. %2,6-di-tert-butyl-para-cresol 0.05 wt. % Composite filler: Monomermixture 20.5 wt. % Barium glass powder 54.5 wt. % (average particle size1.0 ìm) Ytterbium fluoride 25.0 wt. %

EXAMPLE 2 Light-Curing Dental Material (Composite) on the Basis ofComposite Filler

[0072] 39.5 wt.-% of particulate composite material according to example1 was mixed to a homogenous paste with 39.5 wt.-% barium glass powderwith an average particle size of 1.5 μm, 15.5 wt.-% of a monomer mixturewith the composition stated below and 2.5 wt.-% of a bentonite paste.The bentonite paste comprises 12.5 wt.-% bentonite (layered silicate)and 87.5 wt.-% of the monomer mixture. To measure the polymerizationshrinkage using a dilatometer, 0.1 g of the paste were fixed on a smallglass plate, coated with mercury and a distance recorder was placedfloating on the mercury. The paste was lit through the small glass platewith a light polymerization apparatus (500 mW/cm²) for 60 seconds. Apolymerization shrinkage of 1.6% was measured.

Monomer Mixture for the Preparation of the Dental Material

[0073] polymerizable monomers: UDMA 45 wt.-% bisphenol-A-dimethacrylate33.32 wt.-% ethoxylated bisphenol-A 20 wt.-% dimethacrylate Initiatormixture/stabilizer: Camphorquinone DL (Photoinitiator) 0.33 wt.-%4-dimethylamino-benzoic acid- 0.6 wt.-% ethylester (accelerator)2,4,6-trimethylbenzoyl-diphenyl- 0.4 wt.-% phosphine oxide (coinitiator)2,2,6,6-tetramethylpiperidine 0.012 wt.-% -N-oxide Additives: Bluefluorescent pigment 0.04 wt.-% (Lumilux Flu blue)2-(2′-hydroxy-5′-methylphenyl)- 0.3 wt.-% benzotriazole (UV-stabilizer)Composite Monomer mixture 15.5 wt.-% Barium glass powder 39.5 wt.-%(average particle size 1.5 μm) Composite filler 39.5 wt.-% Layeredsilicate paste 2.5 wt.-% (12.5 wt.-% dispersed in monomer mixture)Ytterbiumtrifluoride 3.0 wt.-%

EXAMPLE 3

[0074] A light-curing dental material on the basis of the filleraccording to example 1 was prepared analogously to example 2, but thefiller was not freed of fine and coarse grains by screening. Filler ofthe same batch was used. The polymerization shrinkage was 1.9%.

1. Particulate composite material, characterized in that it has anaverage particle size of 20 to 50 μm and contains at most 10 wt.-%particles with a size of <10 μm.
 2. Particulate composite materialaccording to claim 1, characterized in that it has a maximum particlesize of 70 μm.
 3. Particulate composite material according to claim 1 or2, prepared by curing of a mixture of (a) 10 to 80 wt.-%, preferably 10to 30 wt.-% organic binder; (b) 0.01 to 5 wt.-%, preferably 0.5 to 2wt.-% polymerization initiator; (c) 20 to 90 wt.-%, preferably 60 to 88wt.-% inorganic filler, each relative to the total mass of the uncuredmixture.
 4. Particulate composite material according to claim 3,characterized in that it contains as filler quartz, glass ceramic, glasspowder or a mixture of these.
 5. Particulate composite materialaccording to claim 4, characterized in that it contains glass powder,preferably barium glass powder and/or strontium glass powder. 6.Particulate composite material according to one of claims 4 to 5,characterized in that the quartz, glass ceramic and/or glass powder hasan average particle size of 0.4 to 1.5 μm, preferably 0.7 to 1.0 μm. 7.Particulate composite material according to one of claims 3 to 6,characterized in that it contains 10 to 50 wt.-%, preferably 20 to 30wt.-% X-ray-opaque filler.
 8. Particulate composite material accordingto claim 7, characterized in that it contains ytterbium fluoride. 9.Particulate composite material according to one of claims 3 to 8,characterized in that it contains precipitated mixed oxides. 10.Composition, containing at least one polymerizable monomer and/orprepolymer, at least one polymerization initiator and at least oneparticulate composite material according to one of the previous claims.11. Composition according to claim 10, characterized in that it contains(i) 10 to 80 wt.-% organic binder; (ii) 0.01 to 5 wt.-% polymerizationinitiator; (iii) 20 to 90 wt.-% particulate composite filler accordingto one of claims 1 to 9, each relative to the total mass of thecomposition.
 12. Composition according to claim 10 or 11, characterizedin that it contains inorganic filler as a further component. 13.Composition according to claim 12, characterized in that it contains asinorganic filler quartz, glass ceramic, glass powder, or a mixture ofthese.
 14. Composition according to claim 13, characterized in that itcontains glass powder, preferably barium glass powder and/or strontiumglass powder.
 15. Composition according to claim 13 or 14, characterizedin that the quartz, glass ceramic and/or glass powder has an averageparticle size of 0.4 to 2 μm.
 16. Composition according to one of claims12 to 15, characterized in that it contains 25 to 70 wt.-%, preferably30 to 50 wt.-% quartz, glass ceramic and/or glass powder. 17.Composition according to one of claims 12 to 16, characterized in thatit contains X-ray-opaque filler as a further component.
 18. Compositionaccording to claim 17, characterized in that it contains ytterbiumfluoride.
 19. Composition according to one of claims 17 to 18,characterized in that it contains 1 to 10 wt.-% X-ray-opaque filler. 20.Composition according to one of claims 12 to 19, characterized in thatit contains a layered silicate as a further component.
 21. Compositionaccording to claim 20, characterized in that it contains 0.05 to 5 wt.-%layered silicate.
 22. Composition according to one of claims 10 to 21,characterized in that it additionally contains precipitated mixed oxide.23. Composition according to claim 22, characterized in that it containsSiO₂/ZrO₂ mixed oxide.
 24. Composition according to one of claims 22 to23, characterized in that the mixed oxide has a particle size of 200 to300 nm.
 25. Composition according to one of claims 22 to 24,characterized in that it contains 20 to 70 wt.-% mixed oxide. 26.Composition according to one of claims 10 to 25, characterized in thatit additionally contains 0.01 to 2 wt.-% additives.
 27. Use of acomposition according to claims 10 to 26 as dental material, inparticular as tooth-filling material, material for inlays or onlays,tooth cement, facing material for crowns and bridges, material for falseteeth.